Solving ode for pendulum

Function for pendulum is as follows

function [zdot] = odefun_second_order_pendulum(t,z)



 
% let z = angle

%given data
L=1;
m=1;
b=0.5;
g=9.81;

z1=z(1);
z2=z(2);
zdot(1)=z(2);

zdot(2) =(-b/m)*z2-(g/L)*sin(z1);

zdot = [zdot(1),zdot(2)]\';





end

Below is the program for solving second order ODE.

clear all 
close all
clc

% Solving a second order ODE for pendulum

%z = angle

%Given data

L=1;
m=1;
b=0.5;
g=9.81;

ts = linspace(0,20,100); %timespan 
z0 = [0 3]; % initital conditions

[t,x]= ode45(\'odefun_second_order_pendulum\',ts,z0);

%plotting

figure(1)

plot(ts,x(:,1),\'r\');
hold on
plot(ts,x(:,2),\'b\');
hold on
legend(\'Angular Displacement\',\'Angular Velocity\');
xlabel(\'time\');

saveas(gca,\'Pendulum plot.jpg\');

%animation




x0 = 0;
y0 = 0;

x1 = L*sind(x(:,1));
y1 = -L*cosd(x(:,1));
for i=1:size(x(:,1))
    
    x_1= x1(i);
    y_1= y1(i);
 figure(2)
    plot([x0,x_1],[y0,y_1],\'linewidth\',4,\'color\',\'bla\',\'marker\',\'s\',\'markerfacecolor\',\'g\',\'markersize\',10);
    hold on
    
    rectangle(\'Position\',[-0.05,0,4,0.5],\'Facecolor\',\'blue\');
    line([0 0],[-1.5 1],\'LineStyle\',\'--\',\'linewidth\',2,\'color\',\'bla\')
   
    hold on
     plot(x_1,y_1,\'-o\',\'markerfacecolor\',\'y\',\'markersize\',50);
     
 
     
     plot(x_1,y_1,\'-o\',\'markerfacecolor\',\'bla\',\'markersize\',5);
     
     
     
     hold on
     
    axis([-0.02 0.02 -1.5 0.5]);
    
   Y(i)=getframe(gcf);
     i=i+1;
     hold off
     
     
  drawnow
    
 end
  
movie(Y)
videofile = VideoWriter(\'Simple_Pendulum_Animation.mp4\',\'MPEG-4\');
open(videofile)
writeVideo(videofile,Y)
close(videofile)

Result of Time vs Displacement and velocity plot.

Youtube animation link

https://youtu.be/hVBky00BsG4